"If I die, it will be in the most glorious place nobody has ever seen."

So reads the first sentence of Jill Heinerth's new book, Into the Planet. As a professional cave diver, her relationship with death is more intimate than most. More people have passed away exploring underwater caves than climbing Mount Everest, Heinerth writes, and she herself has had several near-death experiences in the depths of caves and lost friends and mentors under the water. And yet, she keeps going back to some of the last untouched places in the world, lured by beauty, mystery, and the potential for discovery.

I chatted with Heinerth—the first person to dive the ice caves of Antarctica and the female record holder for furthest underwater cave dive—about her life as a diver and the wellness practices that keep her calm in moments of unimaginable chaos. I was surprised to learn about the underwater devastation she's witnessed in her 30-year career, her pre-dive visualization practice, and her ironic fear of gyms. Here are the highlights.

What was going through your mind during your first experience cave diving?

My first experience in an underwater cave was actually really early in my diving career. It was just a baby cave, but I entered into this place called The Grotto up in the Bruce Peninsula in Canada. I was 20 to 30 feet underwater, and my instructor led me into this darkened corridor. And I'm like, Wow, what's this? I could tell in the distance there was a spot of light filtering through the water. I just remember thinking, Oh, this is something I've got to do a lot more! It was almost spiritual, womb-like, you know, being inside Mother Earth.

You've done quite a bit of cave diving since, and your book covers what happens when some of them have gone wrong. What practices help you stay calm during those moments?

When the worst happens—and in an underwater cave that could be suddenly getting engulfed in a white-out where you can't see, or it might be a moment when you've lost visual contact with your safety guideline, or when you're literally wedged stuck in an underwater space, or you've had an issue with your life support equipment—the first thing that happens to your body, obviously, is you kind of go into that fight-or-flight sort of response. Your heart races. And these chattering monkeys just explode in your head.

But in that moment I've learned that you must take a series of deep and slow breaths and literally turn off the emotional side of your brain. That's served me so well, not just in diving but in life in general. Success—or survival in my case—is all about putting together a series of those very small pragmatic, emotionless steps. And after it's all done, and you come out and you go, Wow, the cave tried to keep me today. Then later, you can kind of honor that experience, allow yourself to break down and cry later. Because you still have to process those emotions, or you can become really stuck from trauma.

How do you go about processing a near-death experience like that?

That's an ongoing journey for me, really. I've lost so many friends and colleagues over the years to cave diving and technical diving accidents. My husband says he sees more death in my life than he did from serving in the military. So, for me, it's just trying to honor and remember the good parts or the lessons learned and try to attach each person to something positive.

Are there any mindfulness practices that you do on land that help you in those scary, daunting moments underwater?

Meditation and mindfulness are extremely important in my daily routine, but especially right before a big dive. I sit down, and I take time to close my eyes and mentally pre-visualize anything that can go wrong. What's the worst thing that can happen to me today? And in very specific terms, I walk myself through how I will respond successfully to each one of those possible incidents.

Again, I carry that beyond diving. Anytime I'm doing something new or risky, whether physically risky or personally risky, I ask, What's the worst that can happen to you. Will I get rejected? Mindfully walking through it really helps. And if something goes wrong, you can just say, Oh, I got this. I just practiced this.

The other thing that I always think about pre-dive is my husband, Robert. I remind myself that I'm making choices that are not just for me. The choices that I make could have fallout for my husband, my community, and put other people at risk. That's part of the ritual, too, just thinking, This is not about me. It's about a lot more. And I ask myself in the last moment, Is it worth it? Facing danger, I could lose my life, you know. Is it worth it?

That covers the mental component. How do you physically prepare for big dives?

Diving for a big expedition or a big goal begins years in advance. I'm not one that's really all that thrilled about going to the gym because I start to feel claustrophobic, ironically. So, I cycle a lot, paddle, swim, and I also make sure to sleep. Good nutrition is extremely important. All of that gets me ready for a dive. Everything has to be aligned in order to do a big mission. If one of them is not on, then I'll step back.

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Has being in such a dangerous line of work changed the way you approach your personal relationships?

Absolutely. I'm away a lot, and that's not easy. So when I'm home [with my husband], we really, really appreciate each other. There's not a day that goes by when I don't tell him I love him and vice versa. In some ways, that separation makes our relationship even stronger.

After a dive goes wrong, what keeps you going back to the water?

It's funny. Some people say, "You're fearless," or "You're an adrenaline-junkie." I don't think I'm either of those. There has to be a really good reason. I'm eternally curious, and I really like being involved in projects that matter, science that's important, and goals that have meaning. I want to do something that leaves the world a better place than when I got here—and if that means putting myself in danger at times, to me that's worthwhile.

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What is some of the research that you've helped carry out so far?

There are two areas that I keep getting involved in in my career. One is what I call "Water Literacies." As a cave diver, I'm that canary in the coal mine, going to a place that few people can envision. I'm able to teach people where the water comes from and how they can protect it for future generations. A lot of my scientific collaborations also involve global climate change. Both water issues and global climate change are so interlinked and so critical to the survival of our species, and I hope my adventures and expeditions might give people a chance to enjoy a bit of wonder about the world... And hopefully bring them on board as ocean and environmental advocates, too.

Since you started diving, have you noticed any changes in the water conditions that could be attributed to climate change?

Absolutely. I'm 54 years old, and the changes that I've seen in my 30-year career are terrifying. The coral reefs of my early diving days are mostly dead. The coral's bleached, species are dying off, the ocean is warming, and we're losing the very lungs of our planet that create the oxygen that we breathe. And in the sense of groundwater coming out of caves, the flow has lessened, and the water quality coming out of these caves is declining. It's happening really fast, and when I go to the north, I see very tangible evidence of the loss of sea ice and rising sea levels.

Still, you can go snorkel and be captivated by beauty. But it's changed, and I hope that I can help communicate those changes.

That must be so devastating. I can imagine seeing these changes firsthand creates such a sense of urgency.

Well, even when I first started diving, I remember being swept up in the wonder. But people that were older than me, my mentors, said, "Oh, if you'd only seen it 20 years ago." So, it's all about baselines and personal context. Maybe that's why it's so abstract to the average person. They don't recognize the changes. I hope it doesn't take a catastrophe to shift the hearts and minds of people. I hope instead they might listen to people that spend more time in the outside world or underground world and understand that we have a chance, but it's a very short window we have to make really substantial changes on this planet. It's a really short window.

In your book, you write that we are all explorers. Can you elaborate on that?

The first thing a baby does is put something in its mouth and taste the world. Children are such natural explorers that we have to guide them and hold them back a little bit as parents. I guess I would ask everyone to maybe embrace some of that childlike sense of discovery and exploration and not be so fearful.

Today, I feel like citizens of the world are very fearful. Sure, there's good reason, but I think if we all step toward fear, or darkness, or uncertainty, and make these tiny steps toward things that scare us, we'd learn about something new. That's how we expand the collective mind of humanity.

It's funny that you said gyms make you claustrophobic. What are your other fears outside the water?

I hate things that make me feel like I'm not in control. Driving is one of those because there's this mass of traffic all around me, and I can't always control what people are doing in other vehicles.

But I like taking a really big challenge and figuring out a way through it. There are lots of things in this world that scare me initially, but it's the problem-solving that drives me forward.

What dives are still on your bucket list?

I have kind of an endless bucket list, I guess. I've always wanted to get to the Galápagos and Cocos islands—these really remote, wild places that are still pretty wild. But really, I think a lot of my calling still goes to the purity of exploration—going to places that people haven't been before, haven't documented before. Whether that's inside caves or under the sea ice.

That's really the thing that drives me the most: doing something that hasn't been done before.